A dental handpiece has a bur sleeve for transmitting torque to a dental tool. It is known that rotation of the bur sleeve creates negative pressure inside the handpiece to cause suction of contaminants, such as debris generated during treatment, through an insertion port for a dental tool into the interior of the handpiece. The sucked contaminants may intrude further to a bearing supporting the bur sleeve and located in the proximity of the insertion port, to thereby damage the bearing races and adversely affect smooth rotation of the bearings.
In order to overcome these problems, there is known to provide a bearing seal or a bearing shield in the form of a simple annular plate. The bearing shield engages at one end a groove provided on one of the outer and inner rings of a bearing, and extends toward the other of the rings to cover the bearing. However, the gap between the free end of the shield and the bur sleeve may allow entry of contaminants into the bearing, and thus sufficient blocking effect cannot be achieved.
There have also been proposed dental handpieces having a dust control mechanism. An example of such handpieces is described below with reference to FIG. 3.
FIG. 3 illustrates head 100 of a conventional, angle-type handpiece having a dust control mechanism. The head 100 is of a cartridge type, and is composed of a head body 111 and a cartridge 101 detachably accommodated in the body 111. The cartridge 101 is, in turn, mainly composed of a socket 102, a bur sleeve 112 partly inserted into the socket 102, and upper and lower ball bearings 114 and 115 supporting the bur sleeve 112. The cartridge 101 is fit in the head body 111, with the bur sleeve 112 projecting through a tool insertion port 117.
The dust control mechanism of this handpiece includes a rotary dust control disc 120 fixed on the bur sleeve 112 near the distal end thereof, a stationary dust control disc 121 formed as an extension of the socket 102, and some discharge ports 122 located in the vicinity of the tool insertion port 117. The rotary disc 120 has a flange portion 120a defining a gap between the flange portion and the bur sleeve 112. The stationary disc 121 is inserted into the gap from above the flange portion 120a, to form gaps like a labyrinth.
When the bur sleeve 112 is rotated, negative pressure is created inside the head 100, which causes debris generated during treatment to enter the head 100 through the gap between the tool insertion port 117 and the bur sleeve 112. However, the rotary and stationary discs 120 and 121 prevent the debris from intruding into the ball bearing 115 by physically hitting the debris away or by creating the centrifugal force in the labyrinth, so that the debris is discharged out of the handpiece through the discharge ports 122.
The conventional dust control means provides sufficient advantages in prevention of dust intrusion into the handpiece. However, since the stationary disc 121 is not formed as an independent part, but formed integrally with the bulky socket 101, exchange of the disc 121, when damaged, is not convenient.
There is also known another type of dental handpieces with a dust control mechanism, wherein a stationary dust control disc is formed as an independent part and screwed onto the head. This structure, however, is complex, causing decrease in productivity.